Fuel



July 5, 1960 F. AUDRIETH EIAL 2,943,927

FUEL

Filed March 28, 1949 2 Sheets-Sheet l TEMPERATURE DEGREES CENTIGRADE 'a IO so 40 56 so so PERCENT N2H5NO3 INVENTORS LUDWIG Fl AUDRIETH BY DON W RYKER ATTORNEY y 1960 L- F. AUDRIETH ET-AL I 2,943,927

FUEL

2 Sheets-Sheet 2 Filed March 28, 1949 INVENTORS LUDWIG F: AUDRIETH BY DON W RYKER ATTORNEY United States Patent 9 FUEL Ludwig F. Audrieth, Urbana, and Don W. Ryker, Alton, 111., assignors to Olin Mathieson Chemical Corporation, a corporation of Virginia Filed Mar. 28, 1949, Ser. No. 83,812

8 Claims. (Cl. 52-.5)

This invention relates to internal combustion engine fuels, and more particularly to fuels especially suited for use in engines of the jet-type, such as rocket engines.

The relatively recentadvent of jet propulsion both as applied to launching of rockets in various military devices and in the propelling of heavier-than-air craft has brought with it the need for more efficient fuels than the hydrocarbon-type fuels used in prior internal combustion engines. Of the fuels suggested for this purpose up to the present time, hydrazine, which has the empirical formula N H appears to be the most efficient. Four of the basic requirements for a good rocket fuel are (1) high density, (2) low viscosity, (3) low molecular weight combustion products, and (4) low freezing point. Hydrazine adequately meets the first three requirements but does not meet the fourth requirement because of its high freezing point of 2 C. In operating such rocket engines the hydrazine, or other liquid fuel, is injected into the combustion chamber simultaneously with an oxidant such as hydrogen peroxide, fuming nitric acid, or liquid oxygen in order to effect instantaneous and complete combustion of the fuel. In Alaska and other countries of similar latitude, in the polar regions, and at high altitudes, temperatures of less than 20 C. are commonplace and temperatures as low as -40 C. and lower are frequently encountered. A fuel, therefore, to be satisfactory for use in such climates or at stratospheric altitudes should be capable of maintaining its liquidity at the low temperature prevailing.

An object of this invention is therefore to provide a novel fuel so formulated as to retain its liquidity at low temperatures.

Another object of the invention is to provide a fuel for internal combustion engines which not only has a high density, low viscosity, and gives off combustion products of low molecular weight, but also has a low freezing point.

Still another object is to provide a fuel for internal combustion engines containing hydrazine nitrate as a freezing point depressant especially suited for use in engines of the rocket-type.

Another object is to provide a fuel especially suited for internal combustion engines of the rocket type.

Other objects and advantages will become apparent to those skilled in the art when the following detail description is read in connection with the accompanying drawing, in which Figure 1 is a graph illustrating the freezing point of hydrazine-hydrazine nitrate fuels embodying this invention, and

Figure 2 is a diagram illustrating the freezing point of hydrazine-hydrazine nitrate-water fuels embodying this invention.

In accordance with this invention, it has been found that the above objects and advantages can be obtained by providing as a fuel a mixture of hydrazine nitrate, which has the empirical formula N H NO and hydrazine. By the term hydrazine nitrate as used herein is meant therefore the compound sometimes referred to as hydrazine mononitrate. Hydrazine nitrate, similar to hydrazine, has a high calorific value, decomposes exothermically, does not deleteriously affect the ignitibility of the fuel, and in addition furnishes some of the oxygen required for efiicient combustion thereof.

It is, of course, well-known that the freezing or melting point of a compound is in general lowered by the inclusion therein of an impurity or other compound. In fact the amount of lowering of the freezing point to be expected by a given amount of another compound may be calculated in accordance with the equation which is derived from the Clapeyron equation and Raoults law, wherein n=mole fraction of solute, AH heat of fusion of the solvent, R=gas constant, T: freezing point of the solvent, and T =freezing point of the mixture. Referring to Figure l, the dotted line A indicates the freezing point to be expected by the addition of hydrazine nitrate to hydrazine. The points for this curve A were calculated from the foregoing equation.

It has been discovered, however, that hydrazine nitrate effects an unexpectedly pronounced reduction in freezing point which is illustrated by the curve B in Figure 1. For instance, the maximum lowering of freezing point to be predicted by calculation as shown by curve A, with amounts of hydrazine hydrate up to 50% by weight of the mixture is about 14 C. Actually it has been found that amounts of hydrazine nitrate up to 50% provide a freezing temperature lower than 40 C. Curve B of Figure 1 represents the freezing point of fuels formed by adding various amounts of hydrazine nitrate to substantially pure hydrazine, i.e., 99.6% hydrazine and 0.4% water. The freezing temperatures in degrees centigrade are shown on the ordinate and percentages by weight of hydrazine nitrate in the mixture of hydrazine and hydrazine nitrate are shown on the abscissa. As shown by curve B of Figure l, the hydrazine-hydrazine nitrate fuel of this invention has a freezing point below 20 C. when the hydrazine nitrate content of the mixture is between 29% and 55%. Likewise the hydrazinehydrazine nitrate fuel of this invention has a freezing point below 40 C. when the hydrazine nitrate content of the mixture is in the range of 44% to 50% Amounts of hydrazine nitrate less than about 3% and greater than about 67% in the fuel are of no substantial benefit in lowering the freezing point but may provide some advantage, such as providing oxygen for combustion.

It has also been discovered that some water may be included in the hydrazine-hydrazine nitrate fuel without causing the freezing temperature to become higher. This is of some economic advantage since'hydrazine is produced, in accordance with the methods presently available, in an aqueous solution and although substantially anhydrous hydrazine, i.e. containing about hydrazine, can be produced economically, the production of 99%-100% hydrazine involving removal of the last traces of water is possible at present only at considerable cost. The presence of some water in the hydrazine-hydrazine nitrate fuel does not deleteriously effect the ignitibility of the fuel, but on the other hand large amounts of water are not particularly desirable in the fuel since the water adds nothing to the calorific value thereof.

The diagram shown in Figure 2 illustrates the relationship between freezing point and composition of the ternary system of hydrazine, hydrazine nitrate, and water.

In the diagram the weight percentages of each compo-' nent are represented by the perpendicular distances from each base toward the opposite vertex. Referring vnow to Figure 2, fuels prepared in accordance with this invention have a composition falling within the area defined by thelines AB, BC,-GD, andDA. Hydr,azinehydrazine nitrate compositions falling within this area the fuel greater than 1 to 1 is not desirable.

Fuels having a composition in the range falling within the shaded area of Figure '2 have a freezing point not higher than 20 C. and as indicated in Figure 2 some of the compositions within this rangehave freezing points at temperatures as low as -4D-C. to 50 C. and lower. Such preferred fuels, having a composition fall ing within the .range set forth in the shaded area of Figure 2, are particularly suited for use in frigid climates because of their characteristic low freezing points.

:In view of the great solubility of hydrazine nitrate and water in hydrazine no difficulty is encountered in formulating fuels in accordance with this invention. They may be readily prepared merely by mixing the constituents in such'proportions or amounts as are set forth in-the foregoing, depending upon the freezing point of the fuel desired. The only precautions necessary are those incident with the handling of hydrazine itself, which, as is known in the art, is not only highly inflammable. in the presence of oxygen .but will upon proper ignition such as an electric spark decompose exothermically in the absence of oxygen. For example, a very low freezing point fuel may be prepared in accordance with this invention by employing as a raw material hydrazine which has been dehydrated to a water content of 5% .by weight and mixing therewith an -amount 19f hydrazine nitrate to form 45% by weight of the mixture. The mixing may be accomplished at room temperature and upon solution of the hydrazine nitrate a fuel is obtained having a density at 20 C. of 1.8 and afreezing point below 50 .C. Asillustrated in Figure 2, the components whether they be hydrazine and hydrazine nitrate alone, or hydrazine, hydrazine nitrate, and water, are

mixed .as set .forth above in accordance with any of-the proportions set forth in the shaded area thereof if a fuel 'of very low freezing point is desired. If a fuel having a freezing point from 0 C. .to 20 C; is permissible the proportions may be those set forth inFigure 2 falling outside. the shaded area thereof.

Even when incorporated with other compatible materials, the hydrazineh ydrazine nitrate systems, with or without water, in general continue to exhibit a synergetic depression of the freezing point. The admixture of the usualadditives, for. instance .coloring agents, accelerators, stabilizers,.retardants, or other modifying agents with fuels consisting principally of the hydrazine-hydrazine nitrate mixture, and also the incorporation of the hydra zinc-hydrazine nitrate mixtures with other compatible fuels, is therefore contemplated by the invention. It is also to be understood that although this invention is described in particular with regard to a fuel for an internal combustion .engineot the rocket type, the fuel may likewise find use in other internal combustion engines or the like.

While specific compositions and details have been set forth in the foregoing, it will be understood that various changes may be made without departing from the spirit and scope of this invention and that this invention is therefore not to be limite.d"'to such compositions and details except asset forth in the.v appended claims. 7,

Having thus described theinvention, what is claimed and desired to secure by Letters Patent is:

mixture.

1. A composition of matter consisting essentially of hydrazine with from zero to one part water per part hydrazine by weight included therewith and having as an ingredient dissolved therein a content of hydrazine mononitrate within a range of from about three percent to about sixty-seven percent by weight of the resultant 2. A' composition of matter .consistingiessentially of hydrazine with from zero parts up to one part by weight water per part of the'hydraziue and having as an ingradient dissolved therein a content of hydrazine mononitrate within the range from about twenty-nine percent to fifty-five percent by weight of the resultant mixture;

3. A composition of matter consisting essentially of hydrazine, hydrazine mononitrates, and water in amounts representing a point shown :in the shaded portion of the triangular diagram in Figure 2 of the accompanying drawing. e t

4. A fuel for internal combustion engines consisting essentially of hydrazine having dissolved therein about 44% to hydrazine mononitrate.

5. A fuel :forinternal combustion engines consisting s l y .of-hydrazin with from zero percent up to about .five percent water included therewith and having as an ingredient dissolve therein a vcoutentof ydr zine monon'itrate within the rangev from about twenty-nine percent to fifty-five percent by weight of the resultant mixture. 7

6. A fuel :for internal combusti n engi s onsistin essentially of hydrazine with from zero percent up to aboutzfive percent water included therewith and having as an ingredient dissolved therein a contentof hydrazine mononitrate within the range from about forty-four percent to about fifty percent by weight .of the resultant mixture.

7.'A composition of matter consisting essentially of hydrazine with from about zero percent up to about five percent water, and from about 3% to about 67% hydra zine mononitrate.

8. A composition consisting essentially of hydrazine and from about 3% to about 6.7% .hydrazine'mononitrate. t

References Cited .in the fileofthis patent UNITED STATES PATENTS 2,521,026 'Solomon Sept. 5, 1950 7 OTHER REFERENCES Mellor: Comprehensive Treatise on Inorganic and Theoretical Chemistry, vol. '8, pages 327, 328 (1928), Longmans, Green (30., London. ChemicalAbstracts, vol. 41, page 5700h, Sept. 10, 1947.

Coast Artillery Journal of January-February 1948, page 27, article by Willy Ley. 

1. A COMPOSITION OF MATTER CONSISTING ESSENTIALLY OF HYDRAZINE WITH FROM ZERO TO ONE PART WATER PER PART HYDRAZINE BY WEIGHT INCLUDED THEREWITH AND HAVING AS AN INGREDIENT DISSOLVED THEREIN A CONTENT OF HYDRAZINE MONONITRATE WITHIN A RANGE FROM ABOUT THREE PERCENT TO ABOUT SIXTY-SEVEN PERCENT BY WEIGHT OF THE RESULTANT MIXTURE. 